Duplicating method involving color formation



United States Patent Oflice Patented Apr. 1, 1969 3,435,759 DUPLICATING METHOD INVOLVING COLOR FORMATION Laurence B. Lueck and Ronald I. Morley, St. Paul, Minn., assignors to Dymo Industries, Inc., Berkeley, Calif., a corporation of California No Drawing. Continuation-impart of application Ser. No. 293,892, July 9, 1963. This application Mar. 2, 1966, Ser. No. 531,025

Int. Cl. B41] 27/00; B41m 5/00, 5/22 US. Cl. 101-129 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a process of mimeographing utilizing mimeograph paper carrying a coating of a molybdenum or tungsten water soluble compound wherein the metal ion has a valence of 6 and a buffering agent such as a citrate, and a mimeographing fluid containing a water soluble stannous compound as a reducing agent and citric acid, the molybdenum compounds reacting to provide a blue image while the tungsten compounds provide a yellow image; a brown image can be provided by adding to the mimeograph paper an oxide of phosphorus or silicon or arsenic, a red image can be provided by adding to the mimeograph paper water soluble alkaline thiocyanate or alkyl xanthate, while a black image can be provided by placing one from all three of the compounds named on the one surface; alternatively, the metal compounds may be placed in the mimeographing fluid and the reducing agent can be placed on the mimeograph paper.

This application is a continuation-in-part of the copending application for United States Letter Patent of Laurence B. Lueck and Ronald I. Morley, Ser. No. 293,892, filed July 9, 1963, for Methods and Compositions for Duplicating, now abandoned.

This invention relates to processes for duplicating in visual form subject matter from a master medium to a copy medium, and to improved copy media and developing fluids for use therein, and to improve processes for making the copy media.

Although the subject matter of the present invention is generally useful in all duplicating processes which employ stencils, mats, plates or the like as the master medium to transfer subject matter therefrom to a copy medium, certain important advantages of the invention are more fully realized when applied to mimeographing systems wherein the master medium is a stencil and the copy medium is a sheet of paper. Accordingly, the present invention will be described as applied to a mimeographing system utilizing presently available mimeographing machines and wherein subject matter on a mimeograph stencil is to be duplicated upon mimeograph copy paper.

In certain of the duplicating systems utilized heretofore, inks colored with dyes or pigments have been used to produce the necessary duplication of the subject matter from the stencil onto the copy paper, which inks are not only highly colored but generally are not washable in water. Special cleaning techniques must be used in order to remove such inks from the stencil prior to storage thereof, it being necessary to remove the ink to prevent blocking of the stencil upon drying thereof. The ink in the prior system has also been objectionable in that the equipment is difficult to maintain in a clean and attractive condition, and the ink frequently is advertently placed upon the skin and clothing of the user and upon adjacent surfaces and furniture, it being ditficult .in practice to remove ink thus inadvertently applied.

In certain other prior duplicating systems, so-called spirit duplication systems are utilized which also may produce objectionable straining of the skin and clothes of the user. Many such systems also do not permit the development of a black reproduction of the subject matter from the stencil to the copy paper, such reproduction in black being highly desirable in many instances.

It is an important object of the present invention to provide an improved duplicating process and materials useful therein which is completely clean in that the various solutions utilized therein are substantially colorless whereby the presence of spillage thereof is not objectionable, and wherein the solutions utilized are further. separately water soluble so that any spillage thereof can be readily removed or cleaned.

Another object of the invention is to provide an improved duplicating process of the type set forth which provides a good reproduction of the subject matter of a master medium on the copy medium in a stable black or other colored reproduction, which reproduction has a long life and is highly insoluble in water.

Still another object of the invention is to provide animproved duplicating process of the type set forth in .which there is no offset of the printed subject matter from one copy sheet to the next, whereby clean copy sheets are provided carrying no unwanted printing or smears thereon.

Yet another object of the invention is to provide a duplicating process wherein multicolor duplication can be obtained utilizing a single developing fluid.

Still another object of the invention is to provide a duplicating process which requires no special duplicating equipment, which, is compatible with the inks utilized heretofore and which is generally economical.

A further object of the invention is to provide an improved duplicating medium or copy sheet and an improved process of making the same, all useful in the present invention.

- A still further object of the invention is to provide an improved developing fluid useful in the present invention and replacing the ink utilized heretofore, the developing fluid being substantially colorless and water washable.

Further features of the invention pertain to the particular arrangement of the steps of the processes and to the particular compositions of the solutions and fluids utilized therein whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification.

In accordance with one preferred embodiment of the present invention, subject matter is duplicated from a master medium onto a copy medium utilizing a process comprising the steps of providing a copy medium having on at least one surface thereof a water soluble compound of ametal having a valence number of six and selected from the group consisting of molybdenum and tungsten, providing an aqueous developing fluid containing therein a Water soluble reducing agent for the metal compound, and contacting the metal compound on the one surface of the copy medium with the developing fluid only in areas determined by the master medium to form on the one surface of the copy medium a copy in visual form of the subject matter. Preferably, the water soluble metal compound is present on the copy medium in an amount equal to from about 0.0004 to about 0.008 gram formula weight per square meter thereof while the reducing agent is present in the developing fluid in an amount from about 0.04 to about 1.2 mole per liter; the viscosity of the developing fluid is in the range from about 2,000 to about 30,000 centipoises. It is also desirable to have an acid buffering compound on the surface of the copy medium, and to this end there is applied thereto a water soluble acid buffering compound in an amount from about 0.00027 to about 0.0054 gram formula weight per square meter of surface area, the preferred acid buffering compound being a water soluble citrate compound present in an amount from about 0.001 to about 0.004 gram formula weight per square meter of surface area. The preferred reducing agent is a water soluble stannous compound present in the developing fluid in an amount from about 0.2 to about 0.7 mole per liter. It is also desirable to have a water soluble organic acid in the developing fluid in an amount from about 0.02 to about 0.6 mole per liter, the preferred organic acid being citric acid present in an amount from about 0.1 to about 0.4 mole per liter.

The molybdenum metal compounds yield an intense blue colored copy when reacted with the developing fluid, while the tungsten compounds yield an intense yellow colored copy when reacted with the developing fluid. A good brown colored copy can be produced by modifying the copy medium to incorporate on the treated surface thereof a second water soluble compound containing an ion that is an oxide of an element selected from the group consisting of phosphorus and silicon and arsenic, the preferred concentration of the second Water soluble compound being from about 0.00005 to about 0.005 gram formula weight per square meter of surface area. On the other hand a good red colored copy can be produced by modifying the copy medium to incorporate on the treated surface thereof a third water soluble compound selected from the group consisting of alkaline thiocyanates and alkaline alkyl xanthates, the preferred concentration of the third water soluble compound being from about 0.00013 to about 0.003 gram formula weight per square meter of surface area. A very important feature of the present invention resides in the fact that by a judicious combination of all of the above described ingredients on a copy medium, a very desirable intense black colored copy can be provided, the preferred ratio between the molar concentration of the metal compound and the sum of the molar concentrations of the other two compounds being in the range from about 1.5 to about 5.0, and the ratio between the molar concentrations of the second and third water soluble compounds being in the range from about 1.0 to about 4.0.

In another embodiment of the present invention, the t position of the metal compound and the reducing agent therefor are reversed, i.e., the reducing agent is placed upon the surface of the copy medium and the water soluble metal compound is placed in the developing fluid. The reducing agent is present on the surface of the copy medium in an amount equal to from about 0.0005 to about 0.015 gram formula weight per square meter of surface area, while the metal compound is present in the developing fluid in an amount from about 0.048 to about 1.4 mole per liter. It is also desirable to provide an organic acid on the coated paper, the organic acid being present in an amount equal to from about 0.0003 to about 0.03 gram formula weight per square meter of the surface area.

The following examples are given further to illustrate the invention, but are not to be considered as a limitation thereof but only in further explanation and clarification thereof.

EXAMPLE 1 White mimeograph paper that had been formed on a Fourdrinier paper making machine and dried by hot rollers was passedthrough a starch sizing press in the standard manner. The starch solution in the sizing press had added thereto 0.16 mole per liter of sodium molybdate (Na MoO .2H O) and 0.27 mole per liter of sodium citrate dihydrate. The mimeograph paper in passing through the starch sizing press had applied to only one surface thereof approximately 10 milliliters of the starch solution per square meter of surface area thereof. After the application of the sizing coating, the paper was once again dried on very hot rollers, calendered and wound in the usual manner. There remained on the coated surface of the paper approximately 0.0016 gram formula weight of sodium molybdate per square meter of paper surface and about 0.0027 gram formula weight of sodium cirtate per square meter of paper surface. The coated surface was still white in appearance and was slightly alkaline.

A developing fluid was provided having the following composition:

Ingredient- Percent by weight Water 65.0 Hyonic PE-50 (Nopco Chemical Company) 22.0 Stannous chloride (SnCl .2H O) 8.7 Citric acid, monohydrate 4.3

The resultant developing fluid was essentially colorless and transparent, and was entirely water soluble and water washable. The viscosity of the developing fluid was approximately 9,00() centipoises and it had a pH of about 1.0.

A master was prepared by cutting a stencil to provide thereon the subject matter to be reproduced, after which the stencil was mounted in a Gestetner 320 double drum mimeograph machine in the usual, manner. The copy paper as prepared above was placed in the paper holder with the coated surface thereof disposed toward the inking drum, and the developing fluid was placed in the ink receptacle. Upon operation of the mimeograph 'machine, good copies of the subject matter were made on the coated surface of the copy paper, the subject matter being present on the paper in a visual form as an image of intense blue color at the places where the mimeograph stencil had been cut. There was no offset of the printed matter from one sheet to the next and all of the equipment had the appearance of being freshly cleaned at all times during the use thereof. The colored compound is highly insoluble in Water, i.e., is less than 1% soluble in water, as contrasted to the much higher solubility of the molybdate ion and the stannous ion in water. Tests have proven that the colored compound thus formed is very stable.

The molybdate compound can be applied to the copy paper in ways other than by incorporation in the starch sizing therefor. In fact the molybdate coating can be applied directly to the surface of the copy paper either using the method described above or by means of an air knife coater, by spraying, by dipping, by roll coating, or the like. Also, it will be understood that other copy media than paper can be utilized and specifically other paper products such as cardboard can be utilized, cloth fabrics, synthetic organic plastic resins, wooden surfaces, leather and the like.

The amount of the Water soluble molybdate ion provided on the surface of the copy paper can be widely varied from that illustrated, and in general, any amount from about 0.0004 to about 0.008 gram formula weight per square meter of the surface area coated can be utilized, a preferred range being from about 0.001 to about 0.006 gram formula weight per square meter.

Any suitable source of molybdate ion may be utilized provided that it has a substantial solubility in water, i.e., at least about 1% by weight solubility in water or more. A large number of salts of the molybdate ion have the requisite solubility in water, the following being illustrative: potassium molybdate, lithium molybdate, am

monium molybdate, ammonium paramolybdate, phosphomolybdic acid, berylium molybdate, rubidium molybdate, magnesium molybdate and thallium molybdate.

In the coating composition for applying the reactive coating to the copy paper, the amount of sodium citrate utilized is determined fundamentally by the character of the copy paper substrate being coated, it being desirable to render the coated surface only slightly alkaline and to assist in developing a blue color in the final colored compound. It has been found that the amount of sodium citrate required may vary from as little as about 0.00027 to as much as 0.0054 gram formula weight per square meter of coated surface, a preferred range being from about 0.001 to about 0.004 gram formula weight per square meter of coated surface. Other water soluble acid buffering compounds can be utilized in place of the sodium citrate of Example 1, such as tartrates, salicylates, and the like, care being taken to select a cation in the acid buffering compound that will not form a water insoluble compound with the molybdate ion.

The developing fluid utilized in the Example 1 above is essentially an aqueous solution that is modified to improve the rheological characteristics thereof to make the developing fluid useful in the standard mi-meographing machines. In the developing fluid composition, it is desirable to have at least about fifty percent water in order to have a good development of the color forming compound from the reaction between the molybdate ions and the stannous ions, and the amount of water in the developing fluid may be as much as about seventy percent by weight thereof without unduly interfering with the rheological properties thereof.

The Hyonic PE50 in the developing fluid is nonylphenylethyleneoxide derivative having an average of 4-6 moles of ethyleneoxide therein and serving as a wetting agent and stabilizing additive which improves the flow characteristics of the developing fluid. In place of the Hyonic PE-50, other agents may be utilized to impart to the developing fluid the desired rheological properties. For example, a castor oil emulsion may be used; also useful are the water soluble gums such as gum arabic and guar gum. Starch and certain celluloses such as hydroxyethylcellulose are also useful as are gelatin and certain of the synthetic organic resins such as polyvinyl alcohols and polyvinyl chlorides.

The citric acid utilized in the developing fluid of Example 1 serves to solubilize the stannous chloride and also to stabilize and to intensify the blue color in the reaction product between the molybdate ion and the stannous ion. In fact the color forming reduction reaction preferably takes place in an acid medium, and at least a part of the required acidity is provided by the citric acid. Other useful acids for this purpose are the mineral acids, such as hydrochloric acid, and other organic acids such as tartaric acid and salicyclic acid. When citric acid is utilized, as little as 0.02 mole per liter and as much as 0.6 mole per liter may be provided in the developing fluid, the developing fluid of Example 1 containing 0.25 mole per liter, a preferred range being from about 0.1 to about 0.4 mole per liter.

The above discussed ingredients of the developing fluid all combine toprovide a fluid which has the characteristics essential for use in mimeograph printing and in other forms of stencil duplicating. More specifically, the resultant fluid is a non-film former, i.e., the various ingredients when allowed to dry upon a stencil do not leave a continuous impenetrable film that fills the stencil and will thereafter block passage of the developing fluid therethrough. The resultant developing fluid must also have a viscosity in the expected range of operating temperature (from about 60 F. to about 90 F.) approaching an ideal or Newtonian fluid, the preferred viscosity range being from about 2,000 to about 30,000 centipoises as measured by a Stormer viscosimeter having a cylindrical rotor and a matching cup. If the ink is either dilatant or thixotropic, the ink distribution and passage through the stencil will be adversely affected, i.e., the ink will either feature as it strikes the paper to provide a smudged and blurred image of the subject matter to be reproduced, or the ink will be fed through the stencil so slowly that the image developed is not dark and highly contrasting.

Best color formation is obtained at a low pH on the order of one although a higher pH in the acid range up to about 4 is also useful.

The stannous chloride in the developing fluid of Example 1 comprises about 0.46 mole per liter thereof; as little as 0.046 mole per liter and up to as much as 1.15 mole per liter of stannous chloride may be utilized and still provide highly satisfactory images of the subject matter to be reproduced on the copy paper, this molar range corresponding to a concentration range of 1% to 25% by Weight of the developing fluid. An optimum range for the stannous chloride is from about 0.23 mole per liter to about 0.67 mole per liter which correspond to a concentration range from about 5% to about 15% by weight of the developing fluid.

A number of stannous compounds can be used in the developing fluid of Example 1 in place of the stannous chloride illustrated therein. In general, any water soluble stannous compound may be used, and those compounds particularly useful are stannous fluoride, stannous bromide, stannous iodide, stannous sulfate, stannous acetate and stannous phosphate. Other reducing agents may be utilized in place of the stannous chloride of Example 1, other suitable agents being the water soluble bisulfites, particularly sodium bisulfite; the water soluble thiosulfates, particularly sodium thiosulfate; and organic reducing agents such as ascorbic acid, hydrazine and phenylhydrazine.

In Example 1 above during the color forming reaction, it is believed that molybdenum having a valence number of six in the molybdate ion is reduced by means of the stannous ion and forms a complex highly water insoluble material having the intense blue color noted, it being believed that the atomic ratio of oxygen to molybdenum in the colored complex is greater than 2.5 but less than 3.0. The color of the resultant reaction product can be modified by the addition of certain color modifying agents to the reaction system. A first group of such color modifying agents causes the formation of a brown or sepia reaction product when added to the reaction system, this class of color modifying agents comprising a water soluble compound containing an ion that is oxide of an element selected from the group consisting of phosphorus and silicon and arsenic. In accordance with the present invention, it is desirable to incorporate the color modifying agents on the copy medium as a part of the coating thereon.

The following is an example of the invention wherein a phosphate compound is added to the coating on the copy medium as a color modifying agent.

EXAMPLE 2 A coating solution was formed comprising 0.165 mole per liter of sodium molybdate and 0.07 mole per liter of sodium dihydrogen orthophosphate (NaH PO .H O). The coating solution was applied to one surface of white mimeograph paper at the rate of 10 milliliters of solution per square meter of paper surface. The paper was then dried to provide on the coated surface thereof 0.0016 gram formula Weight of sodium molybdate per square meter and 0.0007 gram formula weight of sodium dihydrogen orthophosphate per square meter. The coated surface was still white in appearance and slightly alkaline, the coating on the paper being in fact colorless and in visible yet highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being brown in color, water insoluble and having a long storage life.

As little as 0.00007 gram formula weight of the phosphate compound per square meter of copy paper can be used successfully (this corresponding to a coating solution concentration of 0.007 mole per liter), and as much as 0.0014 gram formula weight of the phosphate compound per square meter of the copy paper may be used (this corresponding to a concentration of the coating solution of 0.15 mole per liter), a preferred range being from about 0.0004 to about 0.001 gram formula weight per square meter.

Any suitable water soluble phosphate compound may be utilized as a source of the phosphate ion so long as the cation or anion, as the case may be, associated therewith will not react with the molybdate ion to produce a water insoluble compound. Examples of other suitable phosphate compounds are ammonium dihydrogen phosphate and potasium dihydrogen phosphate.

The following is an example of the invention wherein a silicate compound is utilized as a color modifying agent in place of the phosphate compound in Example 2 above.

EXAMPLE 3 A coating solution Was prepared as in Example 2 above substituting 0.03 mole per liter of sodium silicate for the phosphate compound therein, there being on the surface of the treated paper 0.0003 gram formula weight of sodium silicate per square meter thereof. The resultant coated paper was used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being an intense sepia color, Water insoluble and having a long storage life.

As little as 0.00005 gram formula weight of the silicate compound per square meter of a copy paper can be used (corresponding to a coating solution concentration of 0.005 mole per liter), and as much as 0.001 gram formula Weight per square meter may be used (corresponding to a coating solution concentration of 0.1 mole per liter). The silicate compound is more particularly preferred to be present in an amount corresponding to as little as 0.0001 gram formula weight per square meter and up to as much as 0.0005 gram formula weight per square meter. In general any water soluble silica compound is useful, the preferred compounds being the alkali metal and ammonium silicates.

The following is an example of the invention wherein an arsenate compound is substituted for the phosphate compound in Example 2 above.

EXAMPLE 4 A coating solution was prepared as in Example 2 above substituting 0.03 mole per liter of sodium arsenate for the phosphate compound therein, there being on the surface of the treated paper 0.0003 gram formula weight of sodium arsenate per square meter thereof. The resultant coated paper was used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being an intense sepia color, water insoluble and having a long storage life.

As little as 0.00005 gram formula weight of the arsenate compound per square meter of copy paper can be used (corresponding to a coating solution concentration of 0.005 mole per liter), and as much as 0.001 gram formula weight per square meter may be used (corresponding to a coating solution concentration of 0.1 mole per liter). The arsenate compound is more particularly preferred to be present in an amount corresponding to as little as 0.0001 gram formula weight per square meter and up to as much as 0.0005 gram formula weight per square meter. In general any water soluble arsenate compound is useful, the preferred compound being the alkali metal and ammonium arsenates.

In accordance with the present invention, it has further been found that certain compounds act as color modifying agents in the present invention to render the resultant colored image red rather than blue or brown as described above with respect to Examples 1 through 4, these color modifying agents being water soluble compounds selected from the group consisting of alkaline thiocyanates and alkaline alkyl xanthates, the alkyl group in the alkyl xanthates containing from 1 to 5 carbon atoms.

The following is an example of the invention wherein a thiocyanate compound is added to the coating on the copy paper of Example 1 to serve as the color modifying agent.

EXAMPLE 5 A coating solution Was prepared containing 0.165 mole per liter of sodium molybdate and 0.105 mole per liter of ammonium thiocyanate. A white mimeograph paper had applied to one surface thereof the above coating solution at a rate of 10 milliliters of solution per square meter of paper surface, and after drying of the paper, there remained on the coated solution of the paper about 0.00165 gram formula weight of sodium molybdate per square meter of paper and about 0.00105 gram formula weight of ammonium thiocyanate per square meter of paper. The coated surface was white in appearance and slightly alkaline, the coating being colorless and invisible, highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being intense red, Water insoluble and having a long storage life.

As little as 0.00013 gram formula weight of the thiocyanate compound per square meter of copy paper can be used successfully (this corresponding to a concentration of the thiocyanate compound in the coating solution of 0.013 mole per liter), and as much as 0.0025 gram formula weight of the thiocyanate compound per square meter of the copy paper may be used (this corresponding to a concentration of the thiocyanate compound in the coating solution of 0.25 mole per liter). A preferred range of thiocyanate compound is from about 0.001 to about 0.0016 gram formula weight per square meter of coated surface.

Any water soluble thiocyanate compound may be utilized so long as the other ions associated therewith do not react with the molybdate ion to produce a water insoluble compound. Examples of other thiocyanate compounds useful in the present invention are alkali metal compounds, the ammonium compounds and the alkaline earth metal compounds of thiocyanate (hereinafter referred to collectively as alkaline thiocyanates), the preferred specific examples being calcium thiocyanate, potassium thiocyanate, lithium thiocyanate, barium thiocyanate and strontium thiocyanate.

The following is an example of the invention wherein a xanthate compound is substituted for the thiocyanate compound in Example 5 above.

EXAMPLE 6 A coating solution was prepared containing 0.165 mole per liter of sodium molybdate and 0.16 mole per liter of potassium ethyl xantnare. White mimeograph paper was coated on one surface thereof with the coating solution at a rate of 10 milliliters of solution per square meter of paper surface, and after drying of the paper, there remained on the coated surface of the paper about 0.00165 gram formula weight of sodium molybdate per square meter of the paper and about 0.0016 gram formula weight of potassium ethyl xanthate per square meter of paper. The coated surface was white in appearance and slightly alkaline, the coating being colorless and invisible yet highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being intense red, water insoluble and having long storage life.

As little as 0.00016 gram formula weight of the xanthate compound per square meter of copy paper can be used successfully (this corresponding to a concentration of the xanthate ion in the coating solution of 0.016- mole per liter), and as much as 0.003 gram formula weight of the xanthate compound per square meter of the copy paper may be used (this corresponding to a concentration of xanthate ion in the coating solution of 0.3 mole per liter); a yet further preferred range of the xanthate ion of the coated surface of the paper is about 0.0012 to about 0.002 gram formula weight per square meter.

It will be understood that the other water soluble alkaline alkyl xanthates may be utilized in place of the potassium ethyl xanthates utilized in Example 6 so long as the other ions associated therewith will not react with the molybdate ion to produce a water insoluble compound. Specifically other alkali metal ethyl xanthates including lithium ethyl xanthate and sodium ethyl xanthate are useful as well as the ammonium ethyl xanthate. The alkyl group may be other than the ethyl group of Example 6 and in general any alkyl group containing 1 to carbon atoms being useful in the present invention.

Other metal color forming compounds may be utilized in place of the molybdate ion illustrated in Example 1 through 6, the following being an example of the invention wherein tungstate ion is substituted for molybdate ion in Example 1.

EXAMPLE 7 A white mimeograph paper was coated with the solution containing 0.34 mole per liter of sodium tungstate (Na WO -ZH O), the solution being applied at the rate of 10 milliliters of solution per square meter of paper surface, so that upon drying of the coated paper, there remained on the coated surface about 0.0034 gram formula Weight of sodium tungstate per square meter of paper. The coated surface was white and slightly alkaline, the coating being colorless, invisible, highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 1 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being an intense yellow color, water insoluble and having a long storage life.

As little as 0.00035 gram formula weight of the tungstate compound per square meter of copy paper can be used successfully (this corresponding to a concentration of the tungstate compound in the coating solution of 0.035 mole per liter), and as much as 0.007 gram formula weight of the tungstate compound per square meter of the copy paper may be used (this corresponding to a concentration of the tungstate ion in the coating solution of 0.7 mole per. liter); a further preferred range of the tungstate ion on the paper is from about 0.0015 to about 0.0055 gram formula weight per square meter of surface area.

Other sources of tungstate ion may be utilized in place of the sodium tungstate illustrated in Example 7, and in general any water soluble tungstate compound may be used, i.e., any tungstate compound having a solubility in water of at least about 1% by weight or more. Specific examples of other useful tungstate compounds are potassium tungstate, lithium tungstate, ammonim tungstate, ammonium paratungstate, sodium paratungstate, phosphotungstic acid and silicotungstic acid.

It further has been discovered that an important feature of the invention resides in the fact that a suitable combination of blue colored compounds and brown colored compounds and red colored compounds can produce a very satisfactory and highly desirable black compound, i.e., the several types of color modifying agents described above when combined provide a black reproduction in the present invention so as to provide a black image of the material to be reproduced. The following is an example of the invention wherein both brown color modifying agents and red color modifying agents are combined with the basic blue color forming compounds to render a resultant black image.

EXAMPLE 8 There is added to the starch solution in a sizing press 0.4 mole per liter of sodium molybdate, 0.07 mole per liter of sodium dihydrogen orthophosphate and 0.13 mole per liter of ammonium thiocyanate. White mimeograph paper was treated by the sizing press to coat the above solution thereon at a rate of 10 milliliters of solution per square meter of paper surface. After the paper had been dried, there remained on the coated surface thereof 0.005 gram formula weight of sodium molybdate per square meter, 0.0007 gram formula weight of sodium dihydrogen orthophosphate per square meter and about 0.0013 gram formula weight of ammonium thiocyanate per square meter. The coated surface of the paper was still white and slightly alkaline, the coating being colorless, invisible highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fiuid of Example 1 through a stencil onto the treated surface. The image of the subject matter on the stencil was formed on the treated surface of the paper, the image being intensely black, water insoluble and having a long storage life.

The molybdate ion may be present on the surface of the paper in the range from about 0.0004 to about 0.008 gram formula Weight per square meter thereof, a preferred range being from about 0.002 to about 0.006 gram formula weight per square meter. The phosphate ion may be present on the paper in the range from about 0.00007 to about 0.0014 gram formula weight per square meter, a preferred range being from about 0.0004 to about 0.001 gram formula weight per square meter. The thiocyanate ion is present on the surface of the treated paper in the range from about 0.00013 to about 0.0025 gram formula weight per square meter, the preferred range being from about 0.001 to about 0.0016 gram formula Weight per square meter.

In addition, it is necessary that there be a proper balance between the metal ion color forming agents and the color modifying agents present on the surface of the copy medium when the color forming reaction is taking place. More specifically, it is desirable that the ratio of the molar concentration of the molybdate ion to the sum of the molar concentrations of the phosphate and thiocyanate ions be in the range from about 1.5 to about 5.0 and that the ratio between the molar concentrations of thiocyanate ion and the phosphate ion be in the range from about 1.0 to about 4.0. In other Words, there should always be more molybdate ion present than there are color modifying agents on a molar basis so that there will be some blue color formation, and it further is preferred that there be more red color modifying agent present on a molar basis than brown color modifying agent.

It will be understood that any of the various molybdate compounds discussed above with respect to Example 1 may be utilized in Example 8, and likewise that any of the brown color modifying agents including the other phosphates disclosed with respect to Example 2, the silicates disclosed above with respect to Example 3 and the arsenates disclosed above with respect to Example 4 may be utilized in place of the specific phosphate compound set forth in Example 8 above. Further, the other red color modifying agents may be utilized in place of the thiocyanate compound of Example 8, for example the other thiocyanate compounds disclosed above with respect to Example 5 and the various xanthate compounds disclosed above with respect to Example 6.

In each of Examples 1 through 8 above, the metal compound is provided on the copy medium, whereas the reducing agent is present in the developing fluid. In accordance with the present invention, the reverse arrangement is also useful, namely, the reducing agent may be placed on the copy medium and the metal compound may be in the developing fluid.

The following is a specific example of a duplicating process in accordance with the present invention utilizing duplicating materials wherein the metal compound is present in the developing fluid and the reducing agent is initially present on the copy medium.

EXAMPLE 9 White mimeograph paper of the type described above in Example 1 was coated on one surface thereof in the sizing press which had added thereto 0.53 mole per liter of stannous chloride and 0.52 mole per liter of citric acid. The mimeograph paper in passing through the starch sizing press had applied to only one surface thereof approximately 10 milliliters of the coating solution per square meter of surface area thereof, and after drying, there remain'ed on the coated surface of the paper about 0.0053 gram formula weight of stannous chloride and about 0.0052 gram formula weight of citric acid per square meter of paper. The coated surface was white in appearance and slightly acid, the coating being colorless and invisible, highly stable and having a long storage life.

A developing fluid was provided having the following composition:

Ingredient- Percent by weight Water 63.0 Hyonic PE-SO (Nopco Chemical Company) 22.0 Sodium molybdate 10.0 Citric acid 5.0

The resultant developing fluid was essentially colorless and transparent, and was entirely water soluble and water Washable. The viscosity of the developing fluid was approximately 9,000 centipoises and the pH thereof was about 1.0. The sodium molybdate was present in a concentration of about 0.48 mole per liter and the citric acid was present in a concentration of about 0.28 mole per liter.

The resultant coated paper was used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of the present example through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being an intense blue color, water insoluble and having a long storage life.

The amount of stannous chloride provided on the surface of the copy paper can be widely varied from that illustrated, and in general, any amount from about 0.0005

gram formula weight of stannous chloride per square meter (corresponding to a concentration in the coating solution of 0.05 mole per liter), to about 0.015 gram formula weight of stannous chloride per square meter (corresponding to a concentration of coating solution of 1.5 mole per liter) can be utilized, a preferred range being from about 0.005 to about 0.008 gram formula weight per square meter. Other stannous compounds may be utilized, for example, stannous bromide, .stannous iodide, stannous fluoride, stannous sulfate, stannous acetate and stannous phosphate. Furthermore, other reducing agents such as those disclosed above with respect to Example 1 may be utilized in place of the stannous compound of Example 9.

The citric acid in Example 9 is iuseful during the coating operation to maintain the stannous chloride in the ionic form and also to provide an acid medium for the development of the desirable colored complex upon reacting of the stannous compound with the molybdate compound. The amount of citric acid on the surface of the copy paper can be widely varied from that illustrated, and in general, any amount from about 0.0003 to about 0.03 gram formula weight of citric acid per square meter of the surface area coated can be utilized, a preferred range being from about 0.003 to about 0.006 gram formula weight per square meter. Other suitable organic acids may be utilized in place of citric acid including those set forth above with respect to Examples 1 through 8.

The amount of molybdate compound present in the developing fluid may also be varied from as little as 0.048 mole per liter to as much as 1.2 moles per liter, these concentrations corresponding respectively to 1% and 25% by weight of the developing fluid. An optimum range for the molybdate ion is from about 0.24 mole per liter to about 0.72 mole per liter of the developing fluid corresponding respectively to approximately 5% and 15% by weight of the developing fluid. A large number of water soluble molybdate compounds can be used in place of the sodium molybdate in Example 9 above, other specific examples being potassium molybdate, lithium molybdate, ammonium molybdate, ammonium paramolybdate, phosphomolybdic acid, beryllium molybdate, rubidium molybdate, magnesium molybdate, and thallium molybdate. The citric acid in a developing fluid of Example 9 performs the same function and has the same concentration ranges as those disclosed above with respect to the developing fluid of Example 1.

Color modifying agents also can be incorporated in the copy paper of Example 9 above to produce images having colors other than blue. The following is an example of the invention wherein a phosphate compound is added to the coating on the copy medium as a color modifying agent.

EXAMPLE 10 A coating solution was provided comprising 0.53 mole per liter of stannous chloride and 0.07 mole per liter of sodium dihydrogen orthophosphate. The coating solution was applied to one surface of white mimeograph paper at the rate of 10 milliliters of solution per square meter of paper surface. The paper was then dried to provide on the coated surface thereof 0.0053 gram formula weight of stannous chloride per square meter and 0.007 gram formula weight of sodium dihydrogen orthophosphate per square meter. The coated surface was white in color and slightly acid, the coating on the paper being in fact colorless and invisible yet highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 9 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being brown in color, water insoluble and having a long storage life.

As little as 0.00007 gram formula weight of the phosphate compound per square meter of copy paper can be used successfully, and as much as 0.0014 gram formula weight of the phosphate compound per square meter of the copy paper may be used. Any of the suitable water soluble phosphate compounds disclosed above with respect to EX- ample 2 may be utilized in Example 10.

The following is an example of the invention wherein a silicate compound is utilized as a color modifying agent in place of the phosphate compound in Example 1 above.

EXAMPLE 11 A mimeograph paper was made in accordance with Example above but substituting 0.03 mole per liter of sodium silicate for the phosphate compound therein, thereby providing on the surface of the treated paper 0.0003 gram formula weight of sodium silicate per square meter thereof, the coated surface being white and slightly acid. The resultant coated paper was processed through a mimeograph machine as in Example 1 above, utilizing the developing fluid of Example 9 above, and an image having an intense sepia color was produced. The ranges of concentrations of the silicate compounds disclosed above in Example 3 are also useful in Example 11, and the other silicate compounds disclosed above with respect to Example 3 are also useful in Example 11.

EXAMPLE 12 A mimeograph paper was made in accordance with Example 10 above but substituting 0.03 mole per liter of sodium arsenate for the phosphate compound therein, thereby to provide on the surface of the treated paper 0.0003 gram formula weight of sodium arsenate per square meter thereof. The resultant coated paper was processed through a mimeograph machine as in Example 1 above utilizing the developing fluid of Example 9 above, and an image having an intense sepia color was produced. The ranges of concentrations of the arsenate compounds disclosed above in Example 4 are also useful in Example 12, and the other arsenate compounds disclosed above with respect to Example 4 are also useful in Example 12.

The red color modifying agents can also be incorporated in the copy paper of Example 9 above, the following being an example of the invention wherein a thiocyanate compound is added to the coating on the copy paper of Example 9 to serve as a color modifying agent.

EXAMPLE 13 A coating solution was provided comprising 0.53 mole per liter of stannous chloride and 0.13 mole per liter of ammonium thiocyanate. The coating solution was applied to one surface of white mimeograph paper at the rate of 10 milliliters of solution per square meter paper surface. The paper was then dried to provide on the coated surface thereof 0.0053 gram formula weight of stannous chloride per square meter and 0.0013 gram formula weight of ammonium thiocyanate per square meter. The coated surface was white in color and slightly acid the coating on the paper being in fact colorless and invisible yet highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereby by passing the developing fluid of Example 9 through a stencil onto the treated surface. An image of the subject matter on the stencil was formed on the treated surface of the paper, the image being an intense red color, water insoluble and having a long storage life.

As little as 0.00013 gram formula weight of the thiocyanate compound per square meter of paper can be used successfully (this corresponding to a concentration of the thiocyanate compound in the coating solution of 0.013 mole per liter), and as much as 0.0025 gram formula weight of the thiocyanate compound per square meter of the copy paper may be used (this corresponding to a concentration of the thiocyanate compound in the coating solution of 0.25 mole per liter). Any of the suitable water soluble thiocyanate compounds disclosed above with respect to Example 5 may be utilized in Example 13.

The following is an example of the invention wherein an alkyl xanthate compound is utilized as a color modifying agent in place of the thiocyanate compound in Example 13 above.

EXAMPLE 14 A mimeograph paper was made in accodance with Example 13 above but substituting 0.16 mole per liter of potassium ethyl xanthate for the thiocyanate compound therein, thereby providing on the surface of the treated paper 0.0016 gram formula weight of potassium ethyl xanthate per square meter of paper, the coated surface being white and slightly acid. The resultant coated paper was processed through a mimeograph machine as in Example 1 above utilizing the developing fluid of Example 9 above, and an image having an intense red color was produced. The ranges of concentrations of the xanthate compounds disclosed above in Example 6 are also useful in Example 14, and the other xanthate compounds disclosed above with respect to Example 6 are also useful in Example 14.

By adding both a brown color modifying agent and a red color modifying agent to the copy paper of Example 9, a black image can be formed when the developing fluid of Example 9 is applied thereto, the following being such an example in accordance with the present invention.

EXAMPLE 15 There were added to the starch solution in a sizing press 0.53 mole per liter of stannous chloride, 0.07 mole per liter of sodium dihydrogen orthophosphate, 0.13 mole per liter or ammonium thiocyanate and 0.31 mole per liter of citric acid. White mimeograph paper was treated by the sizing press to coat the above solution thereon at a rate of 10 milliliters of solution per square meter of paper surface. After the paper had been dried, there remained on the coated surface thereof 0.0053 gram formula weight of stannous chloride per square meter, 0.0007 gram formula weight of sodium dihydrogen orthophosphate per square meter, 0.0013 gram formula weight of ammonium thiocyanate per square meter and 0.0031 gram formula weight of citric acid per square meter. The coated surface of the paper was still white and slightly acid, the coating being colorless, invisible, highly stable and having a long storage life. The resultant paper was then used in a mimeograph machine of the type set forth in Example 1 above and an image was formed on the treated surface thereof by passing the developing fluid of Example 9 through a stencil onto the treated surface. The image of the subject matter on the stencil was formed on the treated surface of the paper, the image being intensely black, water insoluble and having a long storage life.

The stannous ion may be present on the surface of the paper in the range from about 0.0005 to about 0.015 gram formula weight per square meter thereof, a preferred range being from about 0.005 to about 0.008 gram formula weight per square meter. The phosphate ion may be present on the paper in the range from about 0.00007 to about 0.0014 gram formula weight per square meter, the preferred range being from about 0.0004 to about 0.001 gram formula weight per square meter. The thiocyanate ion may be present on the treated paper in the range from about 0.00013 to about 0.0025 gram formula weight per square meter, the preferred range being from about 0.001 to about 0.0016 gram formula weight per square meter. The citric acid may be present on the surface of the treated paper in the range from about 0.0003 to about 0.03 gram formula weight per square meter.

In addition, it is necessary that there be a proper balance between the reducing agent and the color modifying agents present on the surface of the copy medium. More specifically, it is desired that the ratio of the molar concentration of the stannous ion to the sum of the molar concentrations of the phosphate and thiocyanate ions be in the range from about 1.5 to about 5.0; and that the ratio between the molar concentrations of the thiocyanate ion and the phosphate ion be in the range from about 1.0 to about 4.0. In other words, there should always be more stannous ion present than there are color modifying agents on a molar basis, and it further is preferred that there be more red color modifying agent present on a molar basis than brown color modifying agent.

It will be understood that any of the various reducing agents discussed above with respect to Example 1 can be utilized in Example 15. Likewise any of the brown color modifying agents including the other phosphate disclosed with respect to Examples 2 and 10, the silicates disclosed above with respect to Examples 3 and 11 and the arsenates disclosed above with respect to Examples 4 and 12 may be utilized in place of the specific phosphate compound set forth in Example 15 above. Further, the other red color modifying agents may be utilized in place of the thiocyanate of Example 15, for example, the other thiocyanates disclosed above with respect to Examples 5 and 13 and the various xanthates disclosed above with respect to Examples 6 and 14. Finally, it will be understood that the tungstate compounds of Example 7 may be substituted for the molybdate compounds of Examples 9 through producing a yellow color only.

It will be understood that the various copy media compositions and developing fluid compositions disclosed herein may be utilized in conjunction with different master media and different duplicating processes, i.e., the master media and duplicating process other than those illustrated in the specific examples set forth hereinabove. For example, the master medium, instead of being the stencil set forth in the examples, may be a mat or a plate or other suitable vehicle for carrying subject matter to be reproduced. The developing fluid may be applied in ways other than by a mirneograph machine and may be applied, for example, by printing type members, type ribbons, paints, brushes, spray guns and the like. Rather than first applying a uniform coating to the copy medium the coating applied in accordance with the master medium may first be applied to one surface of an untreated copy medium, after which the developing fluid is applied in a substantially uniform manner over the entire surface of the copy medium so as to provide a visual reproduction of the subject matter on the treated surface of the copy medium.

Because the molybdate compounds produce an essenhally blue image, the tungstate compounds produce a yellow image, the molybdate compounds plus the brown color modifying agents produce brown or sepia colored images,

the molybdate compounds plus the red coloring modifying agents provide red images, and the molybdate compounds with both the brown and red color modifying agents form black images, various combinations of color duplicating can be achieved. For example, if the reducing agent is in the developing fluid, different colored copies of the subject matter on the master medium can be produced simply by using either molybdate treated copy media, or tungstate treated copy media, or media treated with a combination of molybdate compounds and brown color modifying agents, or copy media treated with molybdate compounds and red color modifying agents or copy media treated with molybdate compounds and both brown and red color modifying agents, 5 different colors of copy material being produced interchangeably with the same stencil and the same developing fluid. Alternatively, if the reducing agent is on the paper, the above 5 described different colors of subject matter can be produced by changing the copy media and developing fluid.

From the above it will be seen that there has been provided an improved duplicating process and improved copy media and improved developing fluids for use therein which fulfill all of the objects and advantages set forth above. More specifically an improved duplicating process and materials therefor have been provided that are completely clean in that the various solutions utilized are substantially colorless, whereby the presence of spillage thereof is not objectionable, and wherein the solutions utilized are further separately water soluble so that any spillage thereof can be readily removed or cleaned. Nonetheless, the duplicating process provides a good reproduction of the subject matter on a master medium onto the copy medium in a suitable blue or yellow or brown or red or black colored reproduction thereof, which reproduction has a good storage life and is highly insoluble in water. In the operation of the duplicating process, there is no offset of the printed subject matter from one copy sheet to the next, whereby clean copy sheets are provided carrying no unwanted printing or smears thereon. Furthermore, the duplicating process requires no special duplicating equipment, is compatible with links and materials utilized heretofore, and makes possible multi-color duplication utilizing a single developing fluid. Finally, there is provided an improved duplicating medium or copy sheet together with an improved process of making such a copy sheet, as well as an improved developing fluid for reducing the undesirable inks utilized heretofore, the developing fluid being substantially colorless and water washable.

While there have been described what are at present considered to be certain preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The process of duplicating in visual form subject matter from a master medium to a copy medium, the process comprising the steps of providing a copy medium having on at least one surface thereof a first water soluble compound of a metal having a valence number of six and selected from the group consisting of molybdenum and tungsten and a second water soluble compound selected from the group consisting of alkaline thiocyanates and alkaline alkyl xanthates, providing an aqueous developing fluid containing therein a Water soluble reducing agent for said metal compound, and contacting said water soluble compounds on said one surface of said copy medium with said developing fluid only in areas determined by the master medium to form on said one surface of said copy medium a copy in visual form of the subject matter.

2. The process of duplicating set forth in claim 1, wherein said first water soluble compound is present on said one surface-in an amount from about 0.0004 to about 0.008 gram formula weight per square meter, said second water soluble compound is present on said one surface in an amount from about 0.00013 to about 0.003 gram formula weight per square meter.

3. The process of duplicating in visual form subject matter from a master medium to a copy medium, the process comprising the steps of providing a copy medium having on at least one surface thereof a first water soluble compound of hexavalent molybdenum and a second water soluble compound containing an ion that is the oxide of an element selected from the group consisting of phosphorus and silicon and arsenic and a third water soluble compound selected from the group consisting of alkaline thiocyanates and alkaline alkyl xanthates, providing an aqueous developing fluid containing therein a water soluble reducing agent for said metal compound, and contacting said water soluble compounds on said one surface of said copy medium with said developing fluid only in areas determined by the master medium to form on said one surface of said copy medium a black copy in visual form of the subject matter.

4. The process of duplicating set forth in claim 3, wherein said first water soluble compound is present on said surface in an amount from about 0.0004 to about 0.008 gram formula weight per square meter thereof, said second water soluble compound is present on said one surface in an amount from about 0.00005 to about 0.005 gram formula weight per square meter thereof,

17 and said third water soluble compound is present on said one surface in an amount from about 0.00013 to about 0.003 gram formula weight per square meter thereof.

5. The process of duplicating set forth in claim 4, wherein the ratio between the molar concentration of said first water soluble compound and the sum of the molar concentrations of said second and third water soluble compounds is in the range from about 1.5 to about 5.0, and the ratio between the molar concentrations of said third water soluble compound and said second water soluble compound is in the range from about 1.0 to about 4.0.

6. The process of duplicating in visual form subject matter from a master medium to a copy meduim, the process comprising the steps of providing an aqueous developing fluid containing therein a water soluble compound of a metal having a valence number of siX and selected from the group consisting of molybdenum and tungsten, providing a copy medium having on at least one surface thereof a water soluble reducing agent for said metal compound and a second water soluble compound selected from the group consisting of alkaline thiocyanates and alkaline alkyl Xanthates, and contacting said water soluble compounds on said one surface of said copy medium with said developing fluid only in areas determined by the master medium to form on said one surface of said copy medium a copy in visual form of the subject matter.

7. The process of duplicating set forth in claim 6, wherein said developing fluid contains from about 0.048 to about 1.2 moles per liter of said metal compound, said reducing agent is present on said one surface in an amount from about 0.0005 to about 0.015 gram formula weight per square meter, and said second water soluble compound is present on said one surface in an amount from about 0.00013 to about 0.003 gram formula weight per square meter.

8. The process of duplicating in visual form subject matter from a master medium to a copy medium, the process comprising the steps of providing an aqueous developing fluid containing therein a water soluble compound of hexa'valent molybdenum, providing a copy medium having on at least one surface thereof a water soluble reducing agent for said metal compound and a second 'Water soluble compound containing an ion that is the oxide of an element selected from the group consisting of phosphorus and silicon and arsenic and a third Water soluble compound selected from the group consisting of alkaline thiocyanates and alkaline alkyl Xanthates, and contacting said Water soluble compounds on said one surface of said copy medium with said developing fluid only in areas determined by the master medium to form on said one surface of said copy medium a black copy in visual form of the subject matter.

9. The process of duplicating set forth in claim 8, wherein said developing fluid contains from about 0.048 to about 1.2 moles per liter of said metal compound, said reducing agent is present on said one surface in an amount from about 0.0005 to about 0.015 gram formula weight per square meter thereof, said second water soluble compound is present on said one surface in an amount from about 0.00005 to about 0.005 gram formula weight per square meter thereof, and said third water soluble compound is present on said one surface in an amount from about 0.00013 to about 0.003 gram formula Weight per square meter thereof.

10. The process of duplicating set forth in claim 9, wherein the ratio between the molar concentration of said reducing agent and the sum of the molar concentrations of said second and third water soluble compounds is in the range from about 1.5 to about 5.0, and the ratio between the molar concentrations of said second water soluble compound is in the range from about 1.0 to about 4.0.

References Cited UNITED STATES PATENTS 798,528 8/1905 Ostwald 101-129 1,343,978 6/1920 Little. 2,597,306 5/1952 Eaton et al. 2,663,656 12/1953 Miller et al. 2,864,720 12/1958 Maguire et al. 2,980,551 4/1961 Thomsen. 3,000,298 9/1961 Bryant et al 101-429 FOREIGN PATENTS 687,808 2/1953 Great Britain.

DAVID KLEIN, Primary Examiner.

U.S. Cl. X.R. 

